Kotlin collections

CollectionsTest.kt

fun main() {

    //input data
    val kotlin = Language("kotlin")
    val java = Language("java")
    java.town = "San Francisco"
    val php = Language("php")
    val scala = Language("scala")
    scala.town = "New York"
    val javascript = Language("javascript")
    val languagesList = listOf(kotlin, java, php, scala, javascript)

    // count
    println(languagesList.count()) // 5

    //maxBy
    println(languagesList.maxBy { it.name.length }) // javascript object

    //minBy
    println(languagesList.minBy { it.name.length }) // php object

    //average
    println(arrayOf(8, 8, 10, 9, 9).average()) //8.8

    //sum
    println(arrayOf(7.3, 7.6, 7.4, 7.6, 8.1, 7.7).sum()) //45.7
    println(languagesList.sumBy { it.releaseYear }) // 10050

    //first
    //NoSuchElementException could be thrown
    println(languagesList.first()) // kotlin object
    println(languagesList.first { it.name.length == 3 }) // php object
    println(languagesList.firstOrNull { it.name.length == 2 }) // null

    //find
    println(languagesList.find { it.town == "San Francisco" }) //java object
    println(languagesList.findLast { it.town == "Bucharest" }) //null

    //last
    println(languagesList.last()) // javascript object
    println(languagesList.last { it.town.contains(' ') }) //scala object

    //single
    //IllegalArgumentException if list has more than one element
    println(languagesList.single{ it.town == "San Francisco" }) // java object
    println(languagesList.singleOrNull{ it.town == "Pitesti" }) // null

    //filter
    println(languagesList.filter { it.name.contains('k') }) // list containing kotlin object

    //filterNot(), filterNotNull()
    println(languagesList.filterNot { it.name.contains('k') }) // list of languages other kotlin
    println(languagesList.filterNotNull()) // whole list of languages

    //filterTo(), filterNotTo()
    val listToFilterInto = mutableListOf<Language>()
    languagesList.filterTo(listToFilterInto) { it.town.contains('o') } // list of scala object
    languagesList.filterNotTo(listToFilterInto) { it.town.contains('o') } // list of languages other than scala
    languagesList.filterNotNullTo(listToFilterInto) // list of languages

    //filterIndexed()
    println(languagesList.filterIndexed { index, _ -> index % 3 == 0}) // list of scala

    //map
    println(languagesList.map { it.town }) // list of town
    println(languagesList.mapIndexed { index, language -> index to language.town }) // map of index to town

    //distinct
    println(languagesList.map { it.town }.distinct())

    //associate(), associateBy()
    println(languagesList.associate { it.name to it.town })
//    println(languagesList.associateBy({ it.name }, { it.company }))

    //groupBy()
//    println(languagesList.groupBy { it.company })
}

data class Language(val name: String, var town: String = "default", val releaseYear: Int = 2010)